Elucidating the role of ROS in mediating self-incompatibility induced PCD

自交不亲和性(SI)是开花植物防止自交受精的一种重要机制，否则会导致不必要的近亲繁殖和植物适合性丧失。因此，SI对开花植物的进化成功做出了重大贡献。授粉后，SI利用细胞-细胞识别，通过抑制花粉管生长来阻止自受精，而花粉管生长对将精子细胞输送到雌蕊内的卵细胞至关重要。这涉及雌蕊表达蛋白和同源花粉蛋白之间的高度特异性相互作用，导致识别和抑制遗传相同或自交(不亲和)的花粉，但不识别(亲和)交叉(亲和)花粉。在罂粟(田间罂粟)中，雌蕊的柱头分泌一种小蛋白质(PRSS)，作为信号“配体”。授粉时，PRSS与表达SI受体(PRPS)的“自体”花粉特异性地相互作用，使花粉能够区分“自体”和“非自体”的雌性伴侣。这种相互作用是细胞-细胞识别和决定接受或拒绝的关键步骤，它在不亲和的花粉中触发一个复杂的信号网络，导致花粉管被抑制并被“告知”自杀：“细胞程序性死亡”(PCD)。活性氧物种(ROS)是不稳定的分子，很容易与细胞中的其他分子反应。如果细胞含有过多的这种ROS分子(通常是过氧化氢)，它们会对蛋白质造成损害，甚至可能导致细胞死亡。低水平的顶端局部ROS对于调节花粉顶端的正常生长是重要的。然而，我们已经证明，SI引起花粉管另一部分的ROS水平迅速增加，这些高水平的ROS引发肌动蛋白细胞骨架的变化(对细胞的形状和运动至关重要)，这种类型的ROS增加激活了SI诱导的PCD。我们最近发现，SI诱导的这些高水平的ROS导致一系列不同的花粉蛋白发生变化/破坏，这些蛋白在花粉管生长中发挥重要功能。高水平的ROS分子对蛋白质功能和细胞过程的影响已经在动物中得到了广泛的研究，通常与疾病，特别是癌症有关。然而，我们对高水平的ROS对植物蛋白质的功能及其相关的细胞过程的破坏性影响知之甚少。我们可以在实验室中模拟Papaver SI系统，通过在培养皿中培养花粉管并添加PRSS蛋白来触发SI响应，这为详细研究这些方面提供了一个很好的机会。该项目将利用生化、遗传学和显微镜技术研究SI引发的高水平ROS如何影响一系列选定蛋白质和细胞过程的功能。这些基础研究可能会引起科学界的兴奋，因为它们不仅将为ROS在SI-PCD中的作用提供重要的机制见解，而且还将更广泛地帮助我们理解ROS诱导的植物细胞蛋白质损伤的后果。在实践中，了解SI-PCD涉及的机制可以导致对植物育种有用的应用。肥力和结实对作物产量和粮食安全至关重要。将SI-PCD性状转移到粮食作物中可能有助于植物育种者开发F1杂交种子，从而产生更大、更高产的F1杂交植株，更高效、更经济。目前，生产F1杂交种子采用的是手工去雄的方法，耗时长，成本高。将SI-PCD引入作物物种可以在不进行任何去雄的情况下进行杂交，因为没有自体花粉可以使这些植物受精。因此，利用关于SI-PCD的知识，以高水平的ROS为基本成分，为选育F1杂交作物提供了一种潜在的替代手段。

Self-incompatibility (SI) is an important mechanism used by flowering plants to prevent self-fertilization, which would otherwise result in undesirable inbreeding and loss of plant fitness. For this reason, SI has made a significant contribution to the evolutionary success of flowering plants. After pollination, SI utilizes cell-cell recognition to prevent self-fertilization by inhibition of pollen tube growth, which is crucial for the delivery of sperm cells to the egg cell inside the pistil. This involves a highly specific interaction between a pistil-expressed protein and a cognate pollen protein that results in recognition and inhibition of genetically identical or self- (incompatible) pollen, but not cross (compatible) pollen. In Papaver rhoeas (field poppy), the stigma of the pistil secretes a small protein (PrsS) which acts as a signalling "ligand". Upon pollination, PrsS interacts specifically with "self" pollen expressing the SI receptor (PrpS), allowing pollen to distinguish between "self" and "non-self" female partners. This interaction is the critical step in cell-cell recognition and determining acceptance or rejection which triggers a complex signalling network in incompatible pollen and results in pollen tubes being inhibited and "told" to commit suicide: "Programmed Cell Death" (PCD).Reactive oxygen species (ROS) are unstable molecules that easily react with other molecules in the cell. If a cell contains too many of these ROS molecules (often hydrogen peroxide) they can cause damage to proteins and may even cause cell death. Low levels of tip-localized ROS are important for regulating normal tip growth of pollen. However, we have shown that SI triggers a rapid increase of the ROS levels in another part of the pollen tube and that these high levels of ROS trigger changes of the actin cytoskeleton (crucial for a cell's shape and movement) and that this type of ROS increase activates SI-induced PCD.We recently discovered that these high levels of SI-induced ROS cause changes/damage to a range of different pollen proteins that fulfil important functions in pollen tube growth. The effect of high levels of ROS molecules on protein function and cellular processes has been extensively studied in animals, often in relation to diseases, in particular cancers. However, we know very little about the damaging effect that high levels of ROS can have on the function of plant proteins and their associated cellular processes. The Papaver SI system, that we can mimic in the laboratory by growing pollen tubes in dishes with growth medium and adding the PrsS proteins to trigger the SI response, provides a great opportunity to study these aspects in full detail.Using biochemistry, genetics, and microscopy this project will investigate how high levels of ROS, triggered by SI, affect the function of a range of selected proteins and cellular processes. These fundamental studies are likely to generate excitement in the scientific community as they will not only provide important mechanistic insights into the role of ROS in SI-PCD but also more broadly for our understanding of the consequences of ROS induced protein damage in plant cells. On a practical note, understanding the mechanisms involved in SI-PCD can lead to applications useful to plant breeding. Fertility and seed set are critical for crop yield and thus Food Security. The transfer of SI-PCD traits into food crops could potentially help plant breeders develop F1 hybrid seeds, which produce bigger and more productive F1 hybrid plants, more efficiently and economically. Currently, hand-emasculation is used to produce F1 hybrid seeds, which is time-consuming and expensive. Introducing SI-PCD into a crop species allows it to be crossed without any emasculation, as no self-pollen can fertilize these plants. Thus, utilization of knowledge on SI-PCD, with high levels of ROS as an essential component, provides a potential alternative means to breed F1 hybrid crops.